SQUARE: FF on CUBIC TCP over Links with Different RTT

CUBIC TPC is a congestion control algorithm for TCP. It is the current default TCP algorithm in Linux. Because many Internet servers, such as web servers, are running on Linux operating system, keeping throughput obtained with this TCP algorithm enough is quite important. Then, many performance studies have been published. However, most of these studies were based on network simulators. Thus, evaluations using an actual TCP implementation and actual network elements are important in addition to these existing studies. In this paper, we focus on RTT (round trip time) fairness of CUBIC TCP, which is performance fairness among CUBIC TCP connections with different network delay times. Firstly, we present RTT fairness evaluation using actual TCP implementations and actual network elements and show that the RTT fairness is not enough. Secondly, we discuss the cause of the unfairness based on CUBIC TCP behavior. Thirdly, we propose a method for improving RTT fairness of CUBIC TCP, which is called SQUARE: FF (Feedback for Fairness based on square root of RTT). It has a mechanism with which an insufficient congestion window size is automatically increased. Finally, we present evaluation results and demonstrate that the proposed method provides better fairness than original CUBIC TCP implementation.